Quantification of three macrolide antibiotics in pharmaceutical lots by HPLC: Development, validation and application to a simultaneous separation

A new validated high performance liquid chromatographic (HPLC) method with rapid analysis time and high efficiency, for the analysis of erythromycin, azithromycin and spiramycin, under isocratic conditions with ODB RP18 as a stationary phase is described. Using an eluent composed of acetonitrile –2-methyl-2-propanol –hydrogenphosphate buffer, pH 6.5, with 1.5% triethylamine (33:7: up to 100, v/v/v), delivered at a flow-rate of 1.0 mL min-1. Ultra Violet (UV) detection is performed at 210 nm. The selectivity is satisfactory enough and no problematic interfering peaks are observed. The procedure is quantitatively characterized and repeatability, linearity, detection and quantification limits are very satisfactory. The method is applied successfully for the assay of the studied drugs in pharmaceutical dosage forms as tablets and powder for oral suspension. Recovery experiments revealed recovery of 97.13–100.28%

Iron(II) complexes of tridentate indazolylpyridine ligands: enhanced spin-crossover hysteresis and ligand-based fluorescence.

Reaction of 2,6-difluoropyridine with 2 equiv of indazole and NaH at room temperature affords a mixture of 2,6-bis(indazol-1-yl)pyridine (1-bip), 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine (1,2-bip), and 2,6-bis(indazol-2-yl)pyridine (2-bip), which can be separated by solvent extraction. A two-step procedure using the same conditions also affords both 2-(indazol-1-yl)-6-(pyrazol-1-yl)pyridine (1-ipp) and 2-(indazol-2-yl)-6-(pyrazol-1-yl)pyridine (2-ipp). These are all annelated analogues of 2,6-di(pyrazol-1-yl)pyridine, an important ligand for spin-crossover complexes. Iron(II) complexes [Fe(1-bip)2](2+), [Fe(1,2-bip)2](2+), and [Fe(1-ipp)2](2+) are low-spin at room temperature, reflecting sterically imposed conformational rigidity of the 1-indazolyl ligands. In contrast, the 2-indazolyl complexes [Fe(2-bip)2](2+) and [Fe(2-ipp)2](2+) are high-spin in solution at room temperature, whereas salts of [Fe(2-bip)2](2+) exhibit thermal spin transitions in the solid state. Notably, [Fe(2-bip)2][BF4]2·2MeNO2 adopts a terpyridine embrace lattice structure and undergoes a spin transition near room temperature after annealing, resulting in thermal hysteresis that is wider than previously observed for this structure type (T1/2 = 266 K, ΔT = 16-20 K). This reflects enhanced mechanical coupling between the cations in the lattice through interdigitation of their ligand arms, which supports a previously proposed structure/function relationship for spin-crossover materials with this form of crystal packing. All of the compounds in this work exhibit blue fluorescence in solution under ambient conditions. In most cases, the ligand-based emission maxima are slightly red shifted upon complexation, but there is no detectable correlation between the emission maximum and the spin state of the iron centers

A Water-Stable and Strongly Luminescent Self-Assembled Non-Covalent Lanthanide Podate.

The segmental ligand 2-(6-carboxypyridin-2-yl)-1,1-dimethyl 2-(5-methylpyridin-2-yl)-5,5-methylenebis(1H-benzimidazole) (L9) reacted with an equimolar mixture of LnIII (Ln = La or Eu) and ZnII in basic conditions to give selectively the self-assembled dinuclear non-covalent podates [LnZn(L9 – H)3]2+. Electrospray mass spectrometry and proton NMR spectroscopy show that [LnZn(L9–H)3]2+ adopt the expected head-to-head triple-helical structure with ZnII pseudo-octahedrally co-ordinated by the bidentate binding units of the three segmental ligands and LnIII occupying the remaining facial pseudo-tricapped trigonal prismatic site produced by the wrapped unsymmetrical tridentate units. Upon UV irradiation, solutions of [EuZn(L9 – H)3]2+ in acetonitrile or in water produce strong red luminescence. The Eu (5D0) lifetime and quantum yield indicate that EuIII is efficiently protected from external interactions for complex concentration in the range 10–4–10–8M and that no solvent molecule enters the first co-ordination sphere. Electrospray mass spectrometry combined with high-resolution emission spectroscopy confirm that the structure of the dinuclear triple-helical complex [EuZn(L9 – H)3]2+ is maintained at low concentration which strongly contrasts with the lipophilic analogous non-covalent lanthanide podates [EuZn(Li)3]5+ {i = 7 or 8; 2-[6-(organo)pyridin-2-yl]-1,1-dimethyl-2-(5-methylpyridin-2-yl)-5,5-methylenebis(1H-benzimidazole)} which are decomplexed in acetonitrile for concentrations below 10–5M. Detailed photophysical studies have established that [EuZn(L9 – H)3]2+ works as an efficient UV VIS light-converting device in the solid state and in water

Dissipation of pesticides during composting and anaerobic digestion of source-separated organic waste at full-scale plants

In the present study, concentration levels and dissipation of modern pesticides during composting and digestion at full-scale plants were followed. Of the 271 pesticides analyzed, 28 were detected. Within the three windrows studied, total concentrations were between 36 and 101 μg per kg of dry matter (d.m.) in input materials and between 8 and 20 μg kg d.m.−1 in composts after 112 days of treatment. Fungicides and among them triazoles clearly dominated over other pesticides. More than two-thirds of all pesticides detected in the input materials showed dissipation rates higher than 50% during composting, whilst levels of most triazoles decreased slightly or remained unchanged. The investigation on semi-dry thermophilic anaerobic digestion suggests that pesticides preferentially end up in presswater after solid–liquid separation

Isolated d-f Pairs in Supramolecular Complexes with Tunable Structural and Electronic Properties.

The use of predisposed segmental ligands in multi-component self-assembly processes allows the preparation of triple-helical heterodimetallic d–f complexes in which each pair of metal ions is isolated and protected from external interactions. The selection of the programmed heterodimetallic edifice within the dynamic virtual library arising from the mixture of the reacting components relies on a judicious matching between the stereochemical preferences of the metal ions and the binding abilities of the receptors combined with a reliable characterisation of the thermodynamic equilibria controlling the assembly process. Minor modifications of the receptors (donor groups, peripheral substituents) have considerable effects on formation of heterodimetallic d–f complexes (HHH)-[LnM(L)3] {L = bis[1-methyl-2-(2-pyridyl)benzimidazol-5-yl]methane derivative} thus leading to successive improvements of the stability in aqueous solvent and to the fine tuning of structural and electronic properties. The implementation of specific light-converting properties, thermochromism, switchable magnetism and tunable dynamic behaviour are discussed together with the development of new paramagnetic NMR techniques for characterising lanthanide-containing dimetallic architectures in solution

Unusual electronic effects of electron-withdrawing sulfonamide groups in optically and magnetically active self-assembled noncovalent heterodimetallic d-f podates

The segmental ligand 2-(6-(N,N-diethylcarbamoyl)pyridin-2-yl)-1,1'-dimethyl-2'-(5-(N,N-diethylsulfonamido)-pyridin-2-yl)-5,5'-methylenebis[1H-benzimidazole] (L3) is synthesized via a multistep strategy that allows the selective introduction of an electron-withdrawing sulfonamide group into the ligand backbone and its subsequent hydrolysis to the hydrophilic sulfonate group. Compared to that of the methylated analogue L1, the affinity of the bidentate binding unit of L3 for H+ and for trivalent lanthanide ions (LnIII) in [Ln(L3)3]3+ and [Ln2(L3)3]6+ is reduced because the electron-withdrawing sulfonamide substituent weakens sigma-bonding, but improved retro-pi-bonding between the bidentate binding units of L3 and soft 3d-block ions (M(II) = FeII, ZnII) overcomes this effect and leads to homometallic complexes [Mn(L(i))m]2n+ (i = 1, 3) displaying similar stabilities. Theoretical ab initio calculations associate this dual effect with a global decrease in energy of pi and sigma orbitals when the sulfonamide group replaces the methyl group, with an extra stabilization for the LUMO (pi). The reaction of L3 with a mixture of LnIII and M(II) (M = Fe, Ni, Zn) in acetonitrile gives the noncovalent podates [LnM(L3)3]5+ in which LnIII is nine-coordinated by the three wrapped tridentate segments, while the bidentate binding units provide a facial pseudooctahedral site around M(II). The X-ray structure of [EuZn(L3)3](ClO4)4(PF6)(CH3NO2)3(H2O) reveals that the bulky sulfonamide group at the 5-position of the pyridine ring only slightly increases the Zn-N bond distances as a result of sigma/pi compensation effects. The introduction of spectroscopically and magnetically active FeII and NiII into the pseudooctahedral site allows the detailed investigation of the electronic structure of the bidentate segment. Absorption spectra, combined with electrochemical data, experimentally demonstrate the dual effect associated with the attachment of the sulfonamide group (decrease of the sigma-donating ability of the pyridine lone pair and increase of the pi-accepting properties of the coordinated bidentate binding unit). The influences on the ligand field strength and on tunable room-temperature FeII spin-crossover processes occurring in [LnFe(L3)3]5+ are discussed, together with the origin of the entropic control of the critical temperature in these thermal switches

Influence of Molecular Ordering on Electrical and Friction Properties of omega-(trans-4-Stilbene)Alkylthiol Self-Assembled Monolayers on Au (111)

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